Mars Pathfinder Issues (Updated 9/14/2017)

12. MARS PATHFINDER PRESSURES

For Pathfinder (with an air access tube just 2 mm in diameter), the upper range of the transducer was only 12 mbar during descent, but only 10 mbar on the surface.83

A 10 mbar limit seems very strange given the Viking-2 10.72 mbar pressure seen. Note that the terrestrial dust storm which hit Luke Air Force Base and Phoenix, Arizona on July 5, 2011 increased air pressure by at least 6.6 mbar, and given that both terrestrial and Martian dust storms can turn day to night, the decision to reduce pressure sensitivities of Pathfinder, Phoenix and MSL landers seems highly ill-advised. There remains the question of what happened to the second Pathfinder sensor ordered that could measure up to 1,034 mbar (15 psia) shown on Figure 10B. Perhaps NASA is not as dumb as they seem to be, and they flew that sensor with a program inserted to cut reported pressures to 1% of what it actually measured. We really need to know the final disposition of this transducer, corresponding to Tavis Dash No. 1 on Tavis CAD Diagram 10484.

What were the Pathfinder pressures made public? Lower than expected. MPF landed on July 4, 1997 at an elevation of -3.682 km, most similar to Viking 1 which sat at -3.627 km. For MPF it was late northern summer at Ls 142.7. As noted earlier in Section 7, Schofield et al. (1997)67 indicate that Pathfinder had no pressure data for the most crucial sol – its first operational day on Mars (JPL wiped out all pressure data for the first 9 days of MSL). The reason given by the above reference is there were “various spacecraft software reset and downlink problems.” MPF pressures are shown on Figure 45.

Figure 45: Adapted from Science. Pressures reported by MPF. None is given for the critical landing day.

Two sols worth of MPF hourly pressures are shown on Figure 46 where they are compared to the only sol of published hourly pressure data for MSL.

At first it seemed a bit surprising that MSL and Pathfinder displayed a similar diurnal pressure cycle on Figure 46. Pathfinder had no RTG heater on board. However, the Pathfinder battery was used to heat the probe’s electronics to slightly above the expected nighttime temperatures on Mars.95So again, at local midnight, measured pressures went up because the heater was operating at that time. What was being measured was not ambient pressure. It was just the pressure behind the (likely) clogged dust filter.

With Phoenix, there was a requirement for the lander to wait 15 minutes after the landing before deploying solar panels. This was to allow dust to settle.84 But it is unclear as to whether there was any way to prevent dust from being sucked into the pressure transducer and intermediate dust filter before powering up after the solar panels deployment. Since the dust filter was much smaller on the Phoenix than what was found in the ¼ inch diameter Viking air access tubes, the rate of ingestion of dust up front here is particularly important.

With Phoenix, there was a requirement for the lander to wait 15 minutes after the landing before deploying solar panels. This was to allow dust to settle (http://www.jpl.nasa.gov/news/press_kits/phoenix-launch-presskit.pdf). But it is unclear as to whether there was any way to prevent dust from being sucked into the pressure transducer and intermediate dust filter before powering up after the solar panels deployment. Since the dust filter was much smaller on the Phoenix than what was found in the ¼ inch diameter Viking air access tubes, the rate of ingestion of dust up front here is particularly important.